Project Summary/Abstract Behavioral weight loss treatment (BT), which teaches cognitive and behavioral skills, is the gold standard and first line of treatment for obesity. Outcomes, while clinically significant, are considered suboptimal in that many participants fail to reach and/or maintain the 5 and 10% benchmarks associated with key health benefits. Over the past 30 years, many trials have tested cognitive and behavioral innovations on standard BT skills, but thus far virtually none has produced significantly improved weight losses. Mindfulness and acceptance-based behavioral treatments (MABTs) for obesity is an exception in that rigorous trials have demonstrated considerably greater weight losses for this approach when directly compared to gold standard BT. Yet, MABTs? outcomes have varied, as have their composition. The ability to continue improving and successfully disseminating behavioral treatments for obesity depends on the field increasing its understanding of which MABT components are most efficacious. Consistent with a Phase I of a Multiphasic Optimization Strategy (MOST) approach, we reviewed theoretical accounts of MABTs and identified three key MABT components: (1) Mindful Awareness, (2) Mindful Acceptance, and (3) Values Clarity. Consistent with the second phase of a MOST, this study will utilize a full 2x2x2 factorial design in which 288 overweight/obese participants are assigned to one of eight behavioral weight loss treatments, i.e., representing each permutation of MABT components being included or excluded from the treatment. Due to the ability of a factorial design to pool conditions to examine each main effect, analyses have the same power as a two-arm design. The primary aim of the current study is to evaluate the independent efficacy of mindful awareness, mindful acceptance and values clarity components of MABT on weight loss (at post-treatment and at 6, 12 and 24 months follow-up) over and above standard BT. Secondary aims are to: (1) To evaluate the independent efficacy of mindful awareness, mindful acceptance and values clarity components of MABT on waist circumference, calorie intake, physical activity and quality of life; (2) To confirm that each treatment component impacts the variable which it targets; (3) To test the hypotheses that the efficacy of the treatment components is moderated by susceptibility to internal and external food cues. The exploratory aim is to quantify the component interaction effects, which may be synergistic, fully additive, or partially additive. This study investigates an innovative and especially promising behavioral approach, and will be one of the first to utilize a full factorial design for obesity intervention optimization. Furthermore, it will be the first-ever study to conduct a component analysis to discern independent efficacies of MABT components, and the first to examine interactions of behavioral weight loss components with each other and with baseline characteristics of participants. Results will position the field for future work, i.e., the evaluation of an optimized treatment that can be expected to have superior efficacy and disseminability.